The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combust an air and fuel mixture within cylinders to produce drive torque. A byproduct of combustion is exhaust. The exhaust may include various components, such as nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). An exhaust treatment system includes a catalyst that converts the NOx, CO, and HC to carbon dioxide and water.
A catalyst's conversion of a given component of the exhaust refers to the catalyst's ability to remove the component from the exhaust. A conversion efficiency, such as a NOx conversion efficiency, may be related to a temperature of the catalyst. For example only, NOx conversion efficiency may decrease as the catalyst temperature decreases and vice versa.
The catalyst temperature may be increased in various ways. For example only, heat from the exhaust gas exiting the engine may increase the catalyst temperature. The exhaust gas transfers heat to the catalyst via convection, thereby increasing the catalyst temperature. Fueling to the engine may also be adjusted to increase the catalyst temperature. For example only, unburned fuel from the engine may enter the catalyst, and the catalyst may combust the fuel with oxygen to increase the catalyst temperature. Air may be pumped into the exhaust gas and/or catalyst to increase the amount of oxygen in the catalyst.